A color laser printer including a plurality of photosensitive drums on which electrostatic latent images are formed, and which are provided in parallel with each other and arranged in a predetermined direction is known as an image forming apparatus.
The color laser printer includes a drum unit which holds the photosensitive drums as a single main body. The developing cartridges are detachably mounted in the drum unit. Each of the developing cartridges includes a developing roller, and the developing roller develops an electrostatic latent image which is formed on a corresponding one of the photosensitive drums by supplying toner.
In the drum unit, the plurality of developing cartridges are provided in parallel with each other and arranged in a predetermined direction in a limited space, similarly to the plurality of photosensitive drums.
Since the reduction in size of the color laser printer is desired, the size of the drum unit as a component of the color laser printer needs to be reduced in order to reduce the size of the entire color laser printer.